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Special Photometric Procedures and Multi-step Measurements

5/31/2015 | Susanne Gollor

Table of Contents:

  • General Overview of Measurement & programming principles with photoLab® 7000 Seriesie
  • Programming of Chlorophyll method: step by step
  • Wine quality factors: Colour intensity and nuance
  • Overview of sugar determination principle with enzymatic test kits: Glucose, Sucrose, Fructose

Programms and Programming:

  • Concentrations measurements:
    Programmed methods for commercial test kits User calibration curves e.g. for Uranine
  • Multi-step measurements:
    Chlorophyll methods for environmental analytics, Food (nutrition), R&D…
  • Enzymatic test kits
    available from various manufacturers, complex handling eased by (user-defined) programs
  • Multi-wavelength measurements
    e.g. wine colour

Extense Programming options

         


Programming with photoLab® 7000

Operators, Variables, Conditions…

R = Result
K = Variable in formula, to be defined
A = Absorption A xxxnm

Same absorbance at different steps:
measurements at same wavelength: A xxxnm_2; A xxxnm_3…

F = Key for easy operation:

Operators via F2                    
F1: Back
F4: Next
Variables via F3 (Axxxnm, K1, K2…)
F4: Next

Chlorophyll measurement is needed in many applications:

  • Environmental Analysis
  • Algae content in food & beverage industry
  • Required procedures vary according to application field!

Easy programming according to application requirements

  • Sample preparation according to standard methods:
    Chl is extracted, and a small volume of the extract is measured photometrically
  • The determination of the Chlorophyll is done by measuring the difference of the absorbance before and after adding HCl.
  • The final formula of Chlorophyll take sample and extraction volume into the automatic calculation.

Programming Chlorophyll Measurement:



Here, it is important to indicate the sequence of measurement steps by assigning an index to the absorbance measurement (2, 3…). Subsequently a clear description to each single step can be entered for user-guidance on display.

Using F3 will show an R for Result which can be defined: e.g. for R<0 wrong the resulting display ---- mg/l
To correct condition, use back space until back to left screen               

Wine Colour: An Important Quality Factor

Colour Measurement in Beverage / Wine Industry …

… is important for:

  • Wine growers
  • Third party bottlers’ income quality control.

Photometric colour measurement offers:

  • Accuracy and comparability (versus human eye, comparator …)
  • Reproducibility

Bottlers need several routine testings besides coulor:

  • Testing Water parameters, sugar content, …
  • Turbidity (in many other beverages)
  • COD before disposing water to municipal wastewater plant

Wine Colour = Multi-λ measurement

Wine characterization by colour
Colour Intensity = Sum

Absorbance measurement @ λ 420nm, 520nm and 620nm
Abs420 for yellow/orange/ocker
Abs520 for red
Abs620 for blue (not always included)

R = Abs420 + Abs520 +Abs620
R = Abs420 + Abs520

Colour nuance
Ratio of brown/red nuances < 0,8 violet, 0,8-1,2 red, > 1,2 orange
R = Abs420 /Abs520

Determinations of Sugar (Glu…) with enzymtic test kits, e.g. with

Understanding Enzymtic Test Kits?

Sugar (D-Glu, D-Fru, Sucrose etc.) are important parameters in Wine, Food & Beverage

  • Test kits are based on enzymatic reactions for many substances
  • Enzymes are specific to chemical reactions and substances (substrates)
  • Some tests offer multi-step measurements for determinations of individual sugar molecule concentration such as Sucrose, Glu and Fru
  • Enzymatic test kits are gradually replacing other standard methods
  • Are accepted by many International Organisations in Food & Beverage
  • Enzymes „co-operate“ with metabolistic „energy provider“ (ATP) and Co-enzymes offering a Redox system, here NAD+/NADH and NADP+/NADPH

The Hub: NAD+/NADH co-enzyme:

NAD+/NADH and NADP+/NADPH is a standard step in enzymatic reactions. In reduced form, these redox systems show a peak at 340 nm.

Scheme of Suc, Glu, Fru determination:

Glutotal: Σof Glufree and Glubound
Suc / Fru: Glufree determination before and after „cracking“ of Sucrose

Enzymatic Test Kits …

…. provide:

  • all necessary information on substances to enter formula
  • all enzymes needed
  • all co-enzymes such as NADP+, ATP etc.
  • AQA material

The transfer of reaction into a simplified photometric routine may need several steps and formulae.

Here you can download the whole article as PDF:

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